It is quite easy to get a watt or more with very simple equipment, but to get more than 5 watts becomes a little more difficult. This article describes a 10 watt linear amplifier that is capable of delivering over 15 watts into 50 ohms and uses cheap plastic transistors that are used in CB equipment. If you have difficulty in finding 2SC2078 then lift the lid of your CB set to find a suitable alternative.
The amplifier has a wide bandwidth, from 1.8 MHz through to over 30 MHz. The drive level required is only about 2 - 5 mW under 14 MHz, rising to 10 mW at 30 MHz. You can therefore make a good QRP CW rig with nothing more than this PA and a simple crystal oscillator. I can achieve 12 watts out of mine using a 10-turn loop around my Grid Dip Oscillator!!
The circuit was originally designed to accompany my phasing-type SSB exciter.
To align, set the 1K0 potentiometer to minimum resistance, apply power to the 'PA-12v' and 'DV-12v' terminals whilst monitoring the current drawn by the 'PA-12v' connection. The current should be next to nothing. Increase the potentiometer until it draws about 50 - 100 mA. That's it!!
COILS
L1 - 6 + 6 turns 28 - 36 SWG wire on two ferrite beads superglued
together - side - by side.
L2, L3, L4 - 10 turns 28 - 36 SWG wire on ferrite
bead.
L5 - 4 turns 18 SWG on large ferrite bead.
T1 - 6 turns 24 SWG wire
on two large ferrite beads superglued together - side - by side. Secondary = 1 +
1 turn.
T2 - 3 + 3 turns 18SWG wire on twin-hole ferrite slab. Secondary - 16
turns 22 SWG.
A PCB foil is available. Sorry about the quality, but I drew this before I had a computer. I used pens/film.
Have fun, de HARRY.